1. Field of The Invention
This invention generally relates to an apparatus for controlling the localization (hereunder sometimes referred to as sound image localization) of a sound source image. A sound source image is a listener's acoustic and subjective image of a sound source and will hereunder be referred to simply as a sound image. The control is in such a manner as to make a listener feel that he hears sounds emitted from a virtual sound source (namely, the sound image) which is located at a desired position different from the position of a transducer (for example, a speaker). More particularly a sound-image-localization control apparatus is provided which can be employed by what is called an amusement game machine (namely, a computer game (or video game) device), a computer terminal or the like, and which is reduced in size without hurting the above described listener's feeling about the sound image localization.
2. Description of The Related Art
A conventional sound image localization method employs what is called a binaural technique which utilizes the signal level difference and phase difference (namely, time difference) of a same sound signal issued from a sound source between the ears of a listener and makes the listener feel as if the sound source were localized at a specific position (or in a specific direction) which is different from the actual position of the sound source (or the actual direction in which the sound source is placed).
A conventional sound image localization method utilizing an analog circuit, which was developed by the Applicant of the instant application, is disclosed in, for example, the Japanese Laying-open Patent Application Publication Official Gazette (Tokkyo Kokai Koho) NO. S53-140001 (namely, the Japanese Patent Publication Official Gazette (Tokkyo Kokoku Koho) NO. S58-3638). This conventional method is adapted to enhance and attenuate the levels of signal components of a specific frequency band (namely, controls the amplitude of the signal) by using an analog filter such that a listener can feel the presence of a sound source in front or in the rear. Further, this conventional method employs analog delay elements to cause the difference in time or phase between sound waves respectively coming from the left and right speakers (namely, controls the phase of the signal) such that a listener can feel the presence of the sound source at the left or right side of him.
Further, there has been another conventional sound image localization method realized with the recent progress of digital processing techniques, which is disclosed in, for instance, the Japanese Laying-open Patent Application Publication Official Gazette NO. H2-298200 (incidentally, the title of the invention is "IMAGE SOUND FORMING METHOD AND APPARATUS").
In case of this sound image localization apparatus using a digital circuit, a fast Fourier transform (FFT) is first performed on a signal issued from a sound source to effect what is called a frequency-base (or frequency-dependent-basis) processing, namely, to give signal level difference and a phase difference, which depend on the frequencies of signals, to left and right channel signals. Thus, the digital control of sound image localization is achieved. In case of this conventional apparatus, the signal level difference and the phase difference at a position at which each sound image is located, which differences depend on the frequencies of signals, are collected as experimental data by utilizing actual listeners.
Such a sound image localization apparatus using a digital circuit, however, has drawbacks in that the size of the circuit becomes extremely large when the sound image localization is achieved precisely and accurately. Therefore, such a sound image localization apparatus is employed only in a recording system for special business use. In such a system, a sound image localization processing (for example, the shifting of an image position of a sound of an air plane) is effected at a recording stage and then sound signals (for instance, signals representing music) obtained as the result of the processing are recorded. Thereafter, the effects of shifting of a sound image is obtained by reproducing the processed signal by use of an ordinary stereophonic reproducing apparatus.
Meanwhile, there have recently appeared what is called an amusement game machine and a computer terminal, which utilize virtual reality. Further, such a machine or terminal has come to require real sound image localization suited to a scene displayed on the screen of a display thereof.
For example, in case of a computer game machine, it has become necessary to effect a shifting of the sound image of a sound of an air plane, which is suited to the movement of the air plane displayed on the screen. In this case, if the course of the air plane is predetermined, sounds (or music) obtained as the result of shifting the sound image of the sound of the air plane in such a manner to be suited to the movement of the air plane are recorded preliminarily. Thereafter, the game machine reproduces the recorded sounds (or music) simply and easily.
However, in case of such a game machine (or computer terminal), the course (or position) of an air plane changes according to manipulations performed by an operator thereof. Thus, it has become necessary to perform a real-time shifting of a sound image according to manipulations effected by the operator in such a way to be suited to the manipulations and thereafter reproduce sounds recorded as the result of the shifting of the sound image.
Such a processing is largely different in this respect from the above described sound image localization for recording.
Therefore, each game machine should be provided with a sound image localization device. However, in case of the above described conventional method, it is necessary to perform an FFT on signals emitted from a sound source and the frequency-base processing and to effect an inverse FFT for reproducing the signals. As the result, the size of a circuit used by this conventional apparatus becomes very large. Consequently, this conventional apparatus cannot be a practical measure for solving the problem. Further, in case of the above described conventional apparatus, the sound image localization is based on frequency-base data (namely, data representing the signal level difference and the phase difference which depend on the frequency of a signal). Thus, the above described conventional apparatus has a drawback in that when an approximation processing is performed to reduce the size of the circuit, a head-related transfer function (HRTF) (thus, head-related transfer characteristics) cannot be accurately approximated and that it is not possible to have transfer characteristics correspondingly to all of visual angles from 0 to 360 degrees, which are subtended at a listener's eye.
Namely, as in case of "Interactive Video Game Apparatus" disclosed in the Japanese Laying-open Patent Application Publication Official Gazette NO. H4-242684, sound image localization is effected by preparing only transfer characteristics (namely, coefficients) corresponding to azimuth angles of 90 degrees leftwardly and rightwardly (namely, clockwise and counterclockwise) from the very front of an operator and then performing substantially what is called a pan pot processing on a reproduced sound corresponding to the direction of the very front of the operator and a localization reproduction sound corresponding to each of azimuth angles of 30 degrees leftwardly and rightwardly therefrom (namely, localizing a sound image at an intermediate location by changing the ratio at which the reproduced sound is mixed with the localization reproduction sound).
However, in case of performing such a simple processing, it is difficult to localize a sound image in a large space as subtending a visual angle of more than 180 degrees at a listener's eye (especially, in the rear of the listener).
The present invention is created to eliminate the above described defects of the conventional apparatus.